FIG 1.

Structural model for isoniazid, pyrazinamide, and ethambutol. The dose of each drug is assumed to go through a series of transit compartments (Trans Cmpts) before being absorbed into the central compartment. It is then eliminated from the central compartment with first-order kinetics. An asterisk (*) indicates the peripheral compartment, which applies only to isoniazid and ethambutol. NN, number of transit compartments; V₁, central volume of distribution; Vp, peripheral volume of distribution; Q, intercompartmental clearance; CL, central clearance.